It depends on the policies of the particular DA's office and the attorney's professional relationship with them.
Many prosecutors don't want to hand over police reports until a defense attorney makes a first appearance in court and is formally on the hook for the case. This happens because, unfortunately, some defense attorneys claim they've been hired when the client is still making a decision.
In many of the counties where I practice, it's no problem to get police reports before the arraignment because the prosecutors know that I will not misrepresent my relationship with the defendant, and when I say I've been hired and will be appearing at arraignment, I'll be there.
There are a few, however, where it's virtually impossible to review the reports or talk to the DA before the first appearance.
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this site, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.
Obviously, you want the lawyer who will work the hardest to achieve the best possible results at the earliest opportunity. Personally, I would be a little leery of any attorney who comes too close to promising a specific result at a specific juncture. To suggest that it was "probable" that the charges would be dropped before he's even read the police report appears to me to be promising too much too soon. As of this point all that lawyer has to go on is your side of the story. There is bound to be another side, which the DA will consider before deciding to dismiss. Your prospective lawyer does not even know what that other side is as of this point, so unless you have an airtight alibi or video proof that you did not commit a battery, there is no way to give odds on a DA rejection. If I were you, I would question the optimistic lawyer further to find out why he is so confident that the DA will reject the case. Has he had a case like this before? Does he have a personal relationship with this particular DA such that he "knows" that the DA will reject it? Or is he just telling you what you want to hear?
What is the other lawyer's view on how your case will turn out? Does he agree that the case is so weak that ultimately it will be dismissed?
Why not speak to a third or fourth lawyer? The more lawyers you talk to the more likely you will get a feel for how your case compares to other run of the mill battery charges. A good lawyer will point out the strengths and weaknesses of the prosecutors case and should be able to comment on the strength of your defense.
It is possible to resolve a case pre filing and I have done so but it is unusual. I practice in a busy courthouse (SF) with a well staffed DA unit where charges are often not certain until the arraignment. Sometimes if you are lucky and you know the DAs, you can find out who is going to handle your case and speak to them before they make a filing decision.
I would never, however, promise a client that I could reach the DA, much less settle the case pre filing.